Author(s): G. De Martino; A. Ragone

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Abstract: An experimental investigation of the flow over vertical weirs, referred to as “slot weirs” on account of their markedly elongated rectangular shape, was carried out at the laboratory of the Institute of Hydraulics and Hydraulic Constructions of the University of Naples. Experiments on weirs 3 to 20 mm broad showed that, for heads greater than 6-7 cm and for each weir the coefficient of discharge remains practically constant as the head increases, the constant value being greater the narrower the weir. This finding is accounted for by the combined influence, on the discharge process, of two physical properties of water, namely surface tension and viscosity, and by a possible modification of the kinematic process of contraction, due to the presence of the singular point of contact between outflowing nappe and weir edge. The influence of the above properties of water is enhanced with very small heads (lower than 6 cm), to such an extent as to give rise to sharply different behaviours, depending on the experimental conditions. Specifically, a significant drop in the coefficient of discharge is observed for free nappe weirs, and a sharp increase for fully submerged weirs, both features becoming increasingly more marked as the head decreases. The experimental results are discussed in the light of hydrodynamical considerations on the influence of surface tension and viscosity on the nappe geometry.

DOI: https://doi.org/10.1080/00221688409499369

Year: 1984